A long standing feature request for IKVM has been to make Java collections implement System.IEnumerable and I've always resisted doing that for various reasons.

I while ago -- while discussing this with Stuart Ballard -- I realised that with the proposed C# 3.0 language extensions, in particular "extension methods" it should be possible to make Java collections foreach-able with little effort:

For those who don't know how extension methods work, basically the above code (note the this keyword before the argument type) adds a method to java.util.Collection that feels like an instance method.

Given the way foreach works, I had expected that it too would recognize this GetEnumerator method and therefore work on all Java collections, but alas that is not the case.If you want to see this changed before C# 3.0 is released, please vote. Alternatively, if you're Miguel and on the ECMA C# committee, it should be obvious what to do

A new release candidate based on GNU Classpath 0.91. I did some perf work and a fair bit of restructuring in the way class loaders work, to better support ikvmc and ikvmstub on assemblies loaded in the ReflectionOnly context (on .NET 2.0). The perf work resulted in a significantly improved startup time for Eclipse (IKVM 0.26: 1 minute 23 seconds, IKVM 0.28: 55 seconds).

Updated japi results are available here. The comparison is against JDK 1.5 now and ignores the generics metadata.

Implemented socket timeout by using Socket.Poll() instead of setting the timeout on the underlying socket (because .NET 2.0 considers the socket broken after a Read timed out).

Removed classLoader field from TypeWrapper and made GetClassLoader() abstract (to enable subclasses to use a more efficient way to store the class loader).

Moved creation of java.lang.Class object from TypeWrapper constructor (because it would trigger a call to GetClassLoader before that was ready to return meaningful data and also because it wasn't semantically correct to expose the TypeWrapper instance before it was fully constructed).

Added ikvm.lang.Internal annotation to mark types and members as internal to the assembly (supported by ikvmc only, not in dynamic mode.) Note that ikvm.lang.Internal should only be applied to public types and members. Note also that to reflection these internal types and members will appears as package private.

Removed map.xml hacks to work around cross package accessibility issues (now done by marking the appropriate types/members public and annotating them with @ikvm.lang.Internal).

Hopefully someday Java will support more than the current simplistic scheme where classes are either public or non-public. In the meantime, I've added support to ikvmc for marking classes (and members) as internal (i.e. private to the assembly they live in). By marking a public class with the @ikvm.lang.Internal annotation ikvmc (and IKVM.Runtime.dll) will only allow access to the class by other code also living in the same assembly. I've also added a switch to ikvmc for making an entire package tree internal (the switch is named -privatepackage:<prefix>).

In addition, I've now enabled 1.5 support in the mainline version. Many of the 1.5 APIs that previously were only available on the GNU Classpath generics branch have been ported to the trunk, so it is starting to make more sense to enable 1.5 support in the VM by default.

The code is in cvs, although SourceForge has been having some problems, so it might not yet be available thru anoncvs. Development snapshot binaries are available here.

Yesterday I thought of a potential micro optimization for the generated CIL code. Since I'm now tracking method invocations on the this reference, it is possible to devirtualize calls to final methods or methods that are provably not overridden. I didn't expect too much from this optimization, because I assumed that the .NET JIT is capable of doing the same optimization and so the only effective difference would be the removal of the explict null check of the this reference.

Somewhat to my surprise neither JDK 1.5 Client VM nor the .NET Framework JIT realised that the virtual method invocation could be devirtualized. Unsurprisingly, HotSpot Server VM was able to deduce that the loop didn't actually do anything at all and optimize it away entirely.

I also threw in JDK 1.1, because as usual in microbenchmarks it outperforms HotSpot Client VM.

Note that the use of the equals method in the benchmark is not very significant, it's just a placeholder for a simple method that can easily be inlined. This optimization is most significant for simple property getters that can be inlined.

The code for this optimization is not yet in cvs.

Oops

On a more embarrassing note, doing this optimization also revealed a hole in the object model remapping. Throwable doesn't properly inherit all the Object methods. The code that gets generated works correctly (in most cases), but it is not verifiable. Here's an example of something that is currently broken:

A new release candidate. It turns out I was a little over enthusiastic in restructuring the class loading to move dynamic class loading into a subclass (which I did to make it easier to build a version of IKVM.Runtime.dll that doesn't support dynamic class loading, to run on the Compact Framework). java.lang.reflect.Proxy support requires that you can dynamically load classes in the bootstrap class loader, so I added back support for that (in a hacky way by delegating to a bogus instance of DynamicClassLoader). This bug was reported by Chris Keller who was also kind enough to fix two socket bugs.

Changes:

Restored the ability to dynamically load a class in the bootstrap class loader.

Changed PlainSocketImpl to throw java.net.SocketTimeoutException instead of java.io.InterruptedIOException when a timeout expires.

Changed PlainSocketImpl.read() to return zero instead of throwing an exception when a non-blocking socket read would block.

A new release candidate based on GNU Classpath 0.90 (the successor to 0.20). IKVM.GNU.Classpath.dll grew by more than a megabyte. A big part of this is due to the new crypto implementation that was merged into GNU Classpath. This a great improvement!

This turns out to be caused by a SoftReference that is being cleared too eagerly. Since .NET has no soft references and there is no way to determine if the managed heap is running low, I used a hack to always promote objects referenced by a soft reference to generation 2 and from there on treat them as weak references, which effectively means they will be collected the next time a full GC is run and there are no more strong references to the object. Strictly speaking clearing them before running out of memory is not incorrect, because the Java doc for SoftReference says:

All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError. Otherwise no constraints are placed upon the time at which a soft reference will be cleared or the order in which a set of such references to different objects will be cleared.

However, Eclipse depends on soft references not being cleared (at least during a particular window while it is starting up). I realised that always promoting the object to generation 2 is not correct either (because you may run out of memory before the object gets there). So considering the complexity and possible performance implications of the current hacks, I decided to simply never clear SoftReferences.

In conclusion, the .NET Framework needs something like soft reference support and until that happens, it won't be possible to implement SoftReference correctly and efficiently.

Update: Nat points out in the comments that there is a workaround:

As a workaround, you can start up eclipse with the following command line